UPSTREAM PROCESSINGBioPharm: In implementing QbD, what would you identify as the critical quality attributes (CQAs) in a typical upstream bioprocess using cell-culture?

Vanden Boom (Hospira): Generally, upstream critical quality attributes for a cell-culture manufacturing process are limited to the adventitious agent and bioburden testing of the cell-culture harvest material. This also holds for biosimilar products.

McKnight (Genentech): CQAs are defined for the product, not identified as part of upstream or downstream portions of the manufacturing process. There are key performance indicators (KPIs) that are defined for upstream steps, including culture productivity (i.e., titer), cell growth, and viability. While KPIs may be correlated with CQA results, KPIs are not themselves product quality attributes. However, particular CQAs may be generated or modified during specific upstream or downstream steps. Protein glycosylation, for example, is generally determined during cell culture and minimally altered in downstream unit operations (at least for uncharged glycosylation species). Using this definition of CQAs, those CQAs observed to be potentially impacted during cell-culture steps include product attributes contained within the protein glycan distribution (e.g., afucosylated glycan), charge-variant distribution (e.g., glycated, deamidated forms), and to a lesser extent, molecular-size distribution (e.g., dimer or aggregate forms).

It should be noted that knowledge of an association between cell-culture steps with certain product quality attributes is not a result of implementing a QbD approach but, rather, a result of knowledge gained through the basic scientific and engineering endeavors that should be elements of developing a bioprocess.

Rathore (IIT Delhi): In the past, most CQAs could not be measured directly in the fermenter broth due to the interference from the numerous components present in the broth. As a result of major advancements in analytical science, direct measurements of CQAs are performed in bioprocessing today. These would be product-quality related parameters, including host-cell impurities (e.g., host-cell proteins, DNA), process-related (e.g., Protein A leachate), and product related (e.g., aggregate, basic variants, acidic variants, and glycoxylation pattern). Some of these CQAs, such as glycoxylation pattern for monoclonal antibody (mAb) products, are primarily impacted by the upstream process and are particularly important to monitor during process development.

Weber (CMC Biologics): The goal of a QbD approach is to develop additional knowledge of the impact of upstream process unit operation performance on the final purified product quality. The most likely or desired outcome is to develop a quantifiable correlation between upstream process outputs, such as cell viability or viable cell density (VCD), and product attributes, such as glycosylation. This approach can lead in the determination of CQAs for the cell production bioreactor unit operation. Upstream outputs classified as CQAs have proven to be controversial, because the bioreactor is so far upstream from the final product. However, if a strong correlation can be established between VCD/viability and other CQAs or final product specifications, this can be an appropriate approach.

Girard (Spinnovation): The underlying concept for QbD of an upstream bioprocess is that the desired quality of the biological or biopharmaceutical product is assured every time. CQAs vary for each cell line depending on the nature of the bioprocess, with typical critical qualities such as metabolites and contaminants. CQAs usually include properties that affect product quality and eventually overall performance of the bioprocess. CQAs are typically also release tests, although they don't have to be as there are no real release tests as such in upstream processing.

The variability and complexities associated with the upstream biological process make QbD a complex process, one that relies on defining operation specific critical process parameters (CPPs). CPPs are those likely to impact on the quality of a product or intermediate. For biological products, process control can be difficult to define and implement. O2 pressure, catalyst concentration, and pH are examples of critical parameters. It is important to note that mAbs are currently the leading area of biopharmaceutical research. One of the key parameters to monitor in the implementation of QbD in mAb production is the glycosylation process during formulation. Glycosylation is one of the overriding contributors to mAb heterogeneity and has significant implications for the function of the antibody in vivo and immunogenicity. This means that glycosylation has been isolated as a critical parameter to follow during mAb manufacture. QbD for mAb development with specific glycosylation patterns enables researchers to optimize manufacturing and clinical efficiency.

Johanning (QAtor): The QbD concept works its way back so to speak from the patient to product to process and ultimately to the facility. A risk assessment will outline the risk profile in and between each area.

The starting point for the risk assessment is R&D, which upstream has determined the CQAs on the product. CQAs are often product specifications, including eventual GMP requirements (if GMP is used as part of the biopharmaceutical process, which is often the case in multinational pharma companies in order to ensure a fast-track initiative from R&D to license to operate and market). The risk assessment includes a review and assessment of the products CQAs when manufactured on specific equipment.